The present invention is generally directed to downflow denitrification system utilized to treat water and/or wastewater. More specifically, the present invention is directed to a downflow system utilizing at least two different types of media with multiple bed depths for effective nitrate removal and suspended solid capture.
Treatment of water and/or wastewater, such as sewage, is well known in the art. Treatment systems and methodologies range from simply filtering the water, wastewater, or sewage through a filter bed comprised of sand to spreading the water, wastewater, or sewage and allowing the solids to dry before gathering.
Water and/or wastewater may typically comprise, among other pollutants, nitrogen and suspended solids. It is desirable to remove both nitrogen and suspended solids from treated water and/or wastewater before recycling or reintroducing treated water and/or wastewater into the environment.
Often, for pollution control there are limitations placed on the discharge of nitrogen compounds in treated sewage effluent into streams. Accordingly, much attention has been paid to optimizing denitrification systems. Biologically active filters have become emerging solutions for wastewater treatment facilities that face stringent nutrient regulations with constraints imposed by cold climate conditions or footprint limitations. Such biologically active filters (BAFs) are often more resilient in cold weather conditions when compared to conventional activated sludge systems. Moreover, BAFs require less space, and are often the smallest choice—while maintaining efficient functionality—when compared to alternative systems such as activated sludge and its many variations.
Removal of nitrogen from waste water by the use of nitrifying and denitrifying bacteria generally involves conversion of organic nitrogen and ammonia into nitrates, followed by removal of the nitrates by denitrifying microorganisms to yield nitrogen gas. Converting organic nitrogen and ammonia to nitrates requires adequate aeration and typically results in removal of carbon from the system. Because carbon is required in the denitrification process, it is typically reintroduced into the system by the addition of external carbon source, for example methanol. The introduction of external carbon source generally results in the production of nitrogen gas, carbon dioxide, and water.
Moreover, such biological reduction accomplished by the denitrifying microorganisms occurs on the surface area of the filter media, to which denitrifying microorganisms have attached. Accordingly, it is desirable to provide a filter media that has a large surface area in order to support larger amounts of denitrifying microorganisms. However, such filter media often lacks the ability to effectively capture suspended solids that may also be present in water and/or wastewater.
The use of a filter bed comprising gravel or sand, to which denitrifying microorganisms may be added as a means for treating and denitrifying water and/or wastewater is known in the art. However, in addition to the drawbacks noted above, such deep bed filtration systems are often difficult to use in existing and future treatment facilities because of the large size requirements of such systems. Space restrictions for water and/or wastewater treatment facilities coupled with growing treatment demands as populations grow have resulted in a need for more effective, efficient water or wastewater denitrification systems that occupy a smaller footprint than previous systems.
Accordingly, it is desirable to provide a water and/or wastewater denitrification system that can effectively and efficiently remove both excess nitrates and suspended solids from water and/or wastewater while not increasing the footprint required for such system.